This invention relates to a process for separating linear alpha olefins from saturated hydrocarbons.
Many industrial processes produce olefin/saturated hydrocarbon streams that are mixtures of olefins, saturated hydrocarbons, and oxygenates. Olefins are frequently used in the manufacture of polymers such as polyethylene, as drilling mud additives, or as intermediates for the production of oil additives and detergents. Some industrial processes manufacture olefins streams by oligomerizing ethylene over an alpha olefin catalyst to produce mixtures of alpha and internal olefins having a broad range of carbon numbers. However, these streams rely on the use of ethylene as a feedstock material, which add a significant cost to the manufacture of the olefin. On the other hand, the FT process starts with an inexpensive feedstock, syngas, generally derived from natural gas, coal, coke, and other carbonaceous compounds to make oligomers comprised of olefins, aromatics, saturates, and oxygenates.
The Fisher-Tropsch (FT) process, however, is not very selective to the production of olefins. While reaction conditions and catalysts can be tuned to manufacture a stream rich in the desired species within the FT product stream, a large percentage of the FT stream contains other types of compounds which must be separated from the olefins, which olefins are purified, and then sold into different markets. For example, a typical commercial FT stream will contain a mixture of saturated hydrocarbons, olefins, and oxygenates such as organic carboxylic acids, alcohols, ethers, esters, ketones, and aldehydes. All these compounds must be separated from the crude FT stream before a particular composition may be offered commercially. To further complicate the separation operation, the FT stream contains compounds having a wide spectrum of carbon numbers, as well as a wide variety of olefins, ranging from C2-C200 species, internal linear olefins, alpha linear olefins, internal branched olefins, alpha branched olefins, and cyclic olefins, many of which have similar molecular weights. Separating and isolating these species is no easy task. Conventional distillation methods are frequently inadequate to separate species having close boiling points.
Various processes have been proposed to efficiently separate the different species in a FT stream with sufficient purity that a particular composition is acceptable in the intended application.
It would be desirable to conduct a separation operation on a FT stream in which the activity and life of the separating agent is not diminished by the presence of impurities in the stream, such as oxygenates; which remains active under a wide band of average carbon numbers ranging from C5-C20, and which distinguishes between linear alpha olefins, branched alpha olefins, and paraffins in a FT stream.
U.S. Pat. No. 4,946,560 described a process for the separation of internal olefins from alpha olefins by carrying out a Diels-Alder reaction by contacting a feedstock with an adducting compound such as anthracene to form an olefin adduct (Diels-Alder adduct), separating the adduct from the feedstock, dissociating the olefin adduct through heat to produce anthracene and an olefin composition enriched in alpha olefin, and separating out the anthracene from the alpha olefin.
U.S. Pat. No. 6,184,431 describes a process for the separation of alpha and internal olefins from saturated compounds by contacting a feedstock with a linear polyaromatic compound to form a reaction mixture comprising linear polyaromatic compound-olefin adducts and saturated hydrocarbons, separating the adducts from the saturated hydrocarbons, then dissociating the linear polyaromatic compound-olefin adducts to form linear polyaromatic compounds and an olefin composition.
U.S. Pat. No. 6,271,434 describes a process for the separation of linear alpha olefins from a crude stream containing saturated hydrocarbons, internal olefins, branched olefins, and linear alpha olefins by contacting the feedstock with linear polyaromatic compound to form a reaction mixture comprising linear polyaromatic compound-olefin adducts, separating the adducts from the saturated hydrocarbons and dissociating the adducts to form linear polyaromatic compounds and olefin.
However, it is desirable to obtain a process with economical means to further separate the desired products.
There is provided a process for separating linear alpha olefins from a feedstock composition comprising linear alpha olefins, saturated hydrocarbons, internal olefins, branched olefins, and alcohol comprising:
a) contacting the feedstock composition with a linear polyaromatic compound under conditions effective to form a reaction mixture comprising linear polyaromatic compound-olefins adducts, saturated hydrocarbons, unreacted olefins, and alcohols and unreacted polyaromatic compound;
b) separating the linear polyaromatic compound-olefin adducts from the saturated hydrocarbons, unreacted olefins and alcohol in the reaction mixture to form a hydrocarbon stream comprising saturated hydrocarbons, unreacted olefins and alcohols and an adducted stream comprising the linear polyaromatic compound-olefin adducts and unreacted linear polyaromatic compound;
c) re-equilibrating the adducted stream by partially and selectively dissociating the linear polyaromatic compound-olefin adducts under conditions effective to increase the percentage of the polyaromatic compound reacted with linear alpha olefins over all other olefins reacted with the polyaromatic compound in the stream thereby producing a re-equilibrated stream comprising linear polyaromatic compound-olefin adducts, dissociated olefins, and unreacted and dissociated linear polyaromatic compound;
d) separating the linear polyaromatic compound-olefin adducts from the dissociated olefins in the equilibrated stream to form an olefin stream comprising dissociated olefins and a linear alpha-olefin adducted stream comprising the linear polyaromatic compound-olefin adducts and linear polyaromatic compound;
e) dissociating the linear polyaromatic compound-olefin adducts in the linear alpha olefin adducted stream to form linear polyaromatic compounds and alpha olefin enriched olefin product; and
f) separating the alpha olefin enriched olefin product from the polyaromatic compound,
whereby the alpha olefin enriched olefin product is enriched in the concentration of olefins over the concentration of olefins in the feedstock and enriched in the concentration of linear alpha olefins over other olefins in the feedstock.
Further, a process for separating linear alpha olefins from a Fisher-Tropsch feedstock having an average carbon number in the range of from 6 to 16 and having a predominant olefin species within said range, said feedstock comprising linear alpha olefins, olefins other than linear alpha olefins, saturated hydrocarbons, and alcohols comprising:
a) contacting said feedstock with a linear polyaromatic compound comprising anthracene or benzanthracene under conditions effective to form a reaction mixture comprising linear polyaromatic compound-olefin adducts, unreacted olefins, alcohols, saturated hydrocarbons, and unreacted polyaromatic compound;
b) separating the linear polyaromatic compound-olefin adducts from the saturated hydrocarbons, unreacted olefins and alcohol in the reaction mixture to form a hydrocarbon stream comprising saturated hydrocarbons, unreacted olefins, and alcohols, and an adducted stream comprising the linear polyaromatic compound-olefin adducts and unreacted linear polyaromatic compound;
c) re-equilibrating the adducted stream by partially and selectively dissociating the linear polyaromatic compound-olefin adducts under conditions effective to increase the percentage of the polyaromatic compound reacted with linear alpha olefins over all other olefins reacted with the polyaromatic compound in the stream thereby producing a re-equilibrated stream comprising linear polyaromatic compound-olefin adducts, dissociated olefins, and unreacted and dissociated linear polyaromatic compound;
d) separating the linear polyaromatic compound-olefin adducts from the dissociated olefins in the equilibrated stream to form an olefin stream comprising dissociated olefins and a linear alpha-olefin adducted stream comprising the linear polyaromatic compound-olefin adducts and linear polyaromatic compound;
e) dissociating the linear polyaromatic compound-olefin adducts in the linear alpha olefin adducted stream to form linear polyaromatic compounds and alpha olefin enriched olefin product; and
f) separating the alpha olefin enriched olefin product from the polyaromatic compound,
whereby the alpha olefin enriched olefin product is enriched in the concentration of olefins over the concentration of olefins in the feedstock and enriched in the concentration of linear alpha olefins over other olefins in the feedstock.